1. Field
The present disclosure relates generally to inert gas welding. More particularly, the invention is directed to inflatable purge dams for retaining purge gas around a weld zone.
2. Description of the Prior Art
By way of background, inert gas welding is a species of arc welding in which the molten weld pool is shielded from atmospheric contamination and oxidation by bathing it with an inert gas, such as Argon, or a mixture of Helium and Argon. Popular examples of inert gas welding include TIG (Tungsten Inert Gas) welding and MIG (Metal Inert Gas) welding.
When welding together pipes and other enclosed structures using inert gas welding, it is important to purge the interior of the pipe or structure in the vicinity of the weld zone to prevent corrosion and the formation of oxides on the interior side of the weld pool. Purge dams are conventionally used for this purpose. For example, when butt-welding the ends of two pipe sections to form a consolidated pipe run, two purge dam structures are placed in the pipes, one in each pipe on either side of the weld zone. A purge gas can then be introduced into the area between the dams.
One well-known purging device used for pipe welding applications is the inflatable purge dam. As shown in FIG. 1, an inflatable purge dam typically include a pair of inflatable purge dam bladders 2 and 4 mounted on a purge gas delivery tube 6. The inflatable bladders usually comprise an inner bladder made from a resilient gas-impermeable material (such as latex rubber), and an outer protective cover made from fabric or other material (such as nylon) to protect the inner bladder from welding heat and caustic chemicals. The purge gas delivery tube is apertured inside the inflatable bladders so that the bladders will inflate when a purge gas “PG” is introduced. The purge gas delivery tube includes a pressure-sensitive gas discharge valve 8 located in the weld zone 10 that exists between the bladders. The discharge valve is designed to open when the purge gas reaches a predetermined pressure that is sufficient to inflate the bladders and ensure that the bladders form effective weld zone seals with the inside walls of the pipes P1 and P2 to be welded. Once the weld zone seals have been formed, the discharge valve will open, thereby releasing purge gas into the weld zone. An air vent tube 12 typically extends through one of the bladders. The vent tube vents air from the weld zone as it is displaced by the purge gas, and may be connected to oxygen monitoring equipment for monitoring the oxygen content within the weld zone.
Conventional inflatable purge dam devices as described above are sold in a fully assembled state. They come in different sizes for use in pipe installations of different nominal pipe size (NPS). Applicants have observed that if one of the purge bladders ruptures, it must either be repaired or an entire new assembly must be purchased. Applicants have further observed that there are certain welding applications wherein existing inflatable existing purge dam apparatus are not satisfactory, either because the pipe installation requires that the two purge bladders be of different size, or because the separation distance between the purge bladders is not optimal. In such cases, there is nothing the welder can do other than to use what is at hand. Applicants have additionally observed that there are occasions wherein only one purge bladder is needed rather than two, such as when only one of the pipes needs to be blocked. Accordingly, applicants submit that there is presently a need for improvement in the construction of inflatable purge dams. What is required in particular is an inflatable purge dam apparatus that can be easily repaired if one of the purge bladders ruptures, or which can be used in non-standard pipe installations where existing apparatus are not optimal, or which can be used for applications where only one purge bladder is required.